1. Field of the Invention
The invention relates to a chair, more particularly to a chair which is provided with a locking unit for locking a backrest or a seat relative to a stationary frame after adjustment of an angle between the backrest or the seat and the stationary frame.
2. Description of the Related Art
Referring to FIGS. 1 to 3, a conventional chair 1 is shown to include a chair seat 130, a backrest 140, a backrest support arm 16, a backrest bracket 161, a seat frame 15, a linking member 121, and a locking unit 17.
As illustrated, the seat frame 15 is disposed under the seat 130, and has opposite left and right sidewalls 151,152. The backrest bracket 161 is disposed rearwardly of the seat frame 15, and has an upper portion 1611 disposed between and pivoted to the left and right side walls 151,152 of the seat frame 15 so as to be turnable relative to the seat frame 15.
The backrest support arm 16 has a top connected to the backrest 140, and a bottom connected to the backrest bracket 161 so as to be turnable therewith.
The linking member 121 has a front part disposed between the left and right side walls 151,152 of the seat frame 15 and formed with an arcuate slot 123 defined by a slot defining wall, and a rear part connected to a lower portion 1612 of the backrest bracket 161 so as to be movable therealong.
The locking unit 17 includes a stationary clamping seat 18, a movable bolt 122, a movable clamping member 125, a cam member 171, and an operating lever 172. The stationary clamping seat 18 is mounted on the right side wall 152 of the seat frame 15, has a clamping end 180 disposed between the right side wall 152 and the front part of the linking member 121. The movable bolt 122 has opposite left and right ends, and extend through the left and right side walls 151,152 of the seat frame 15, the clamping end 180 of the stationary clamping seat 18, and the arcuate slot 123 in the linking member 121 in such a manner that the slot-defining wall moves relative to the movable bolt 122 so as to prevent interference between the linking member 121 and the movable bolt 122 when the linking member 121 turns together with the backrest bracket 161 relative to the seat frame 15. The movable clamping member 125, which is in the form of a tubular sleeve, is sleeved on the movable bolt 122 so as to be movable therewith. The cam member 171 is pivoted to the seat frame 15 via a pivot 175, and has two cam faces 173,174 for abutting against a head end of the movable bolt 122. The operating lever 172 is fixed to and extends outwardly from the cam member 171. The operating lever 172 is turnable downwardly about the pivot 175 so as to move the movable bolt 122 to a locking position, in which the bolt 122 is urged by a high strength coil spring 124 to move toward the right side wall 152 and to abut against the cam face 174, and in which a clamping end of the movable clamping member 125 cooperates with the clamping end 180 of the stationary clamping seat 18 to provide a clamping force to clamp the linking member 121 so as to immobilize the linking member 121 relative to the seat frame 15 and so as to prevent turning of the backrest bracket 161 with respect to the left and right side walls 151,152 of the seat frame 15. The operating lever 172 is turnable upwardly about the pivot 175 so as to move the movable bolt 122 to an unlocking position, in which the cam face 173 abuts against the head end of the movable bolt 122, and in which the movable bolt 122 moves against the urging force of the spring 124 toward the left side wall 151 of the seat frame 15 so as to release the linking member 121 from being clamped between the movable clamping member 125 and the stationary clamping seat 18.
Some disadvantages encountered during use of the aforesaid conventional chair 1 are as follows:
In order to move the movable bolt 122 between the locking and unlocking positions, a high strength coil spring 124 is employed in the conventional chair. Such type of spring 124 is costly to manufacture. In addition, the spring 124 will suffer from spring fatigue after long term use and will, in turn, affect the locking effect of the locking unit 17.
Furthermore, the cam member 171 has to be manufactured from a high strength material, such as metal, so as to withstand the high compression force of the spring 124. As such, the manufacturing cost is relatively high.
The object of this invention is to provide a chair that is provided with a locking unit which can be manufactured from low cost materials so as to eliminate the aforesaid disadvantages resulted.
Accordingly, a chair of the present invention includes a seat frame, a backrest bracket, a backrest support arm, a linking member, and a locking unit. The seat frame has opposite left and right side walls. The backrest bracket is disposed rearwardly of the seat frame, and has an upper portion disposed between and pivoted to the left and right side walls so as to be turnable relative to the seat frame. The backrest support arm has a bottom connected to the backrest bracket so as to be turnable together therewith. The linking member has a front part which is disposed between the left and right side walls of the seat frame and which is formed with an arcuate slot, and a rear part which is connected to a lower portion of the backrest bracket so as to be movable therewith. The locking unit includes a stationary clamping seat, a movable bolt, a movable clamping member, a generally C-shaped connector, and an operating lever. The stationary clamping seat is mounted on the right side wall of the seat frame, and has a clamping end that is disposed between the right side wall and the front part of the linking member. The movable bolt has opposite left and right ends, and extends through the left and right side walls of the seat frame, the clamping end of the stationary clamping seat, and the arcuate slot which permits the linking member to move past the movable bolt without interfering the movable bolt when the linking member turns with the backrest bracket relative to the seat frame. The movable clamping member is mounted on the movable bolt, and has a clamping end that is disposed between the left side wall of the seat frame and the front part of the linking member so as to be movable along with the movable bolt. The C-shaped connector has a left section connected to the right end of the movable bolt at a contact point, and a right section. The operating lever has a left end pivoted to the right section of the C-shaped connector about a first pivot, and a left extension which extends from the left end of the operating lever toward the left section of the C-shaped connector and which is pivoted to the right side wall of the seat frame about a second pivot. The second pivot extends parallel to the first pivot, and is located between the left and right sections of the C-shaped connector. The operating lever is turnable upwardly and downwardly so as to move the movable bolt via the C-shaped connector between a locking position, in which the clamping end of the movable clamping member cooperates with the clamping end of the stationary clamping seat to provide a clamping force to clamp the linking member so as to immobilize the linking member relative to the seat frame and so as to prevent turning of the backrest bracket with respect to the left and right side walls of the seat frame, and an unlocking position, in which the movable bolt moves toward the left side wall of the seat frame so as to release the linking member from being clamped between the movable clamping member and the stationary clamping seat. When the movable bolt is at the locking position, the linking member counteracts the clamping force, which results in a pulling force that pulls the left end of the operating lever in a direction toward the left side wall along a horizontal line defined by the movable bolt. Under this condition, the second pivot and the contact point of the C-shaped connector cooperatively define an imaginary line that extends in a direction transverse to the horizontal line and that is disposed above the first pivot so that the operating lever is prevented from being turned upwardly by the pulling force.